Granular detergent compositions have so far been principally prepared by spray drying. In the spray drying process the detergent components, such as surfactants and builders, are mixed with as much as 35-50% heated and spray dried, which is expensive. A good agglomeration process, however, could be less expensive.
Spray drying requires 30-40 wt. % of the water to be removed. The equipment used to produce spray dry is expensive. The granule obtained has good solubility but a low bulk density, so the packing volume is large. Also, the flow properties of the granule obtained by spray drying are adversely affected by large surface irregularities, and thus the granulate has a poor appearance. There are other known disadvantages in preparing granular detergents by spray drying.
There are many prior art nonspray-drying processes which produce detergent granules. They have drawbacks as well. Most require more than one mixer and a separate granulation operation. Others require use of the acid form of the surfactant to work. Some others require high temperatures which degrade the starting materials. High active surfactant paste is avoided because of its stickiness.
High shear and cold mixing processes per se are known, but they require an extra grinding step or some other action. E.g., some use a dry neutralization technique of mixing an acid form of the surfactant with sodium carbonate. See, e.g., U.S. Pat. No. 4,515,707, Brooks, issued May 7, 1985; Japanese laid-open Appln. No. 183540/1983, Kao Soap Co., Ltd., filed Sept. 30, 1983; and Japanese Sho. 61-118500, Lion K.K., June 5, 1986. Typically, excess carbonate is required (2-10 molar excess) to assure reasonable conversion of the surfactant acids. Excess carbonate adversely drives up the wash water pH to the very alkaline range which can be undesirable, particularly for some nil-phosphate formulas.
Also, the use of a surfactant acid requires immediate use or cool temperature storage, for highly reactive acids such as the alkyl sulfate acids are subject to degradation unless cooled, they tend to undergo hydrolysis during storage, forming free sulfuric acid and alcohol. In practical terms, such prior art processes require close-coupling of surfactant acid production with granulation which requires an additional capital investment.
Another reason for not desiring to use the acid form of the surfactants in some applications is the potential degradation of other formula ingredients (e.g., tripolyphosphate converting to the less soluble pyrophosphate species).
In U.S. Pat. No. 4,162,994, Kowalchuk, issued July 31, 1979, it is disclosed that calcium salts are required to overcome problems in processing by nonspray drying (i.e., mechanical) means formulations based on sodium salts of anionic surfactants and certain nonionic surfactants. A drawback to that process is that insoluble calcium salts can lower the solubility of the formulation, which is of particular importance in stress situations, such as in pouch-type executions.
An important object of the present invention is to make a dense, concentrated detergent granular product by an agglomeration process as opposed to a spray-drying process. Other objects of the present invention will be apparent in view of the following.